1. Field of the Invention
The present invention relates to a solid-state image capturing device for performing photoelectric conversions on and capturing image light from a subject, which is composed of a semiconductor element, such as a MOS image sensor. Further, the present invention relates to an electronic information device, such as a digital camera (e.g., digital video camera and digital still camera), an image input camera, a scanner, a facsimile machine and a camera-equipped cell phone device, having the solid-state image capturing device as an image input device used in an image capturing section of the electronic information device.
2. Description of the Related Art
In recent years, a MOS image sensor using a MOS (Metal Oxide Semiconductor) has begun to be widely used as a conventional solid-state image capturing device, along with a CCD (Charge Coupled Device) image sensor. That is because the MOS image sensor can be downsized and its operation can be sped up by being integrated with a peripheral circuit for driving a sensor using a conventional IC manufacturing method. Further, that is because the MOS image sensor has an advantage of having a simpler structure and the MOS image sensor does not require a high driving voltage, compared to the CCD image sensor.
Unlike the CCD image sensor, the MOS image sensor reads out a signal charge from a photodiode, which functions as a photoelectric conversion section, by converting it into an image capturing signal. Therefore, for each pixel, a charge detection section (charge voltage conversion section; floating diffusion FD) and a plurality of transistors are used, the plurality of transistors constituting a signal readout circuit for amplifying a signal voltage according to the signal voltage detected by the charge detection section. For example, a MOS image sensor in general requires, for each pixel, four transistors, namely a charge transfer transistor, a reset transistor, an amplifying transistor, and a selection transistor, which constitute a signal readout circuit; a photodiode functioning as a light receiving element that constitutes a light receiving section; a charge detection section; and a signal readout circuit. As a result, it is difficult to miniaturize the pixel of the MOS image sensor.
Recently, a charge detection section (floating diffusion FD) and a signal readout circuit are shared by a plurality of light receiving section as a multiple pixel sharing structure, and circuit driving that does not require a selection transistor is conceived as a signal readout circuit. Further, it is conceived that the number of transistors per pixel is reduced to control the deterioration of characteristics for the miniaturization of pixels.
FIG. 8 is a top view schematically illustrating a conventional pixel arrangement of a two pixel sharing structure.
As illustrated in FIG. 8, a conventional MOS image sensor 100 has a two pixel sharing structure, in which a light receiving sections 101 and 102 are paired and arranged in a longitudinal direction. Gate electrodes 103 and 104, for respective charge transfer transistors are provided at the adjacent and opposing corner portions in the rectangular-shaped light receiving region of the light receiving sections 101 and 102. The gate electrode 103 is driven and a signal charge is transferred from the light receiving section 101 to a shared floating diffusion FD. In addition, the gate electrode 104 is driven and a signal charge is transferred from the light receiving section 102 to a shared floating diffusion FD. The signal charge is converted into a signal voltage by the floating diffusion FD. The converted signal voltage is amplified in accordance with the signal voltage by a signal readout circuit (not shown) to be output to a signal line as an image capturing signal. Above the light receiving sections 101 and 102, color filters (not shown) of respective colors are provided. When the color arrangement for such color filters is the Bayer arrangement, the colors of the color filters (not shown) correspond, for example, to “B (blue color)” for the light receiving section 101, “G (green color)” for the light receiving section 102, “R (red color)” for the light receiving section on the right of the light receiving section 102, and “G (green color)” for the light receiving section on the right of the light receiving section 101.
FIG. 9 is an enlarged top view schematically illustrating one pixel structure in the solid-state image capturing device in FIG. 8.
In FIG. 9, a method for selecting a pixel by X and Y addresses to read a signal charge, and for selecting a pixel through two, the upper and lower layers (first layer and second layer) of metal wiring layers is used in general in the conventional MOS image sensor 100. For example, in FIG. 9, the wiring in the Y direction (longitudinal direction) is illustrated as a first layer of a metal wiring layer 111, and the wiring in the X direction (transverse direction) is illustrated as a second layer of a metal wiring layer 112. The gate electrode 103, which constitutes the charge transfer transistor, is put across the lower right corner portion of the light receiving section 101. The signal charge is transferred from the light receiving section 101 to the floating diffusion FD through a channel region below the gate electrode 103 by applying a transfer control voltage to the gate electrode 103. Note that a third layer of a metal wiring layer 117, which will be described later, is not shown here.
FIG. 10 is a longitudinal cross sectional view of two pixels in the A-A′ direction in FIG. 9.
In FIG. 10, a P-type well region 115 is formed on an N-type substrate 114. The light receiving section 101, which is composed of an N-type layer that constitutes a photodiode, and a P-type separation region 116 as pixel separation layers, which has a higher concentration than the P-type well region 115, are provided in the P-type well region 115. In addition, The first layer of the metal wiring layer 111, the second layer of the second wiring layer 112, and the third layer of the metal wiring layer 117 are provided in an interlayer insulation film 118, as wiring layers that connect each element for operating the light receiving section 101 functioning as a pixel to read out a signal. Further, a color filter for each color is provided above the pixel in a corresponding manner to the light receiving sections 101 and 102. A microlens 120 for focusing light on the respective light receiving sections 101 and 102 is provided on the color filter 119. Note that the second layer of the metal wiring layer 112 described above is not illustrated here.
In this case, the circumference of the light receiving section 101 and the gate electrode 103 at the lower right corner portion are limited by the two longitudinally oriented lines of the first layer of the metal wiring layer 111 and the two transversely oriented lines of the second layer of the metal wiring layer 112, such that incident light enters the light receiving section 101 and the gate electrode 103 in a plan view. Thus, the way to avoid covering the light receiving section 101 by the metal wiring layer is to reduce shielding the light receiving section as much as possible and maximize the opening above so as to secure the amount of incident light onto the light receiving section 101.
As a technique similar to the structure according to the present invention, Reference 1 is proposed, where a portion of a wiring layer surrounds above and avoid covering a photodiode such that incident light does not enter the peripheral section of the photodiode.
In Reference 1, a thick, multilayer wiring layer and an interlayer insulation film exist between a photodiode and a shielding film that is provided to avoid covering the photodiode. Even if a peripheral section of the photodiode is attempted to be shielded by the shielding film, the distance between the photodiode and the shielding film is long. Therefore, the incident light that enters, from an opening of the shielding film provided above the photodiode goes around and enters the peripheral section of the photodiode. This will result in a smear. In order to prevent such a smear, another solid-state image capturing device is proposed, where a portion of a wiring layer under a shielding film is positioned so that a light entering region is further reduced and limited. As a result, light will not enter a transistor in a peripheral section of the photodiode, and the opening of the shielding film is further narrowed to be shielded, thereby reducing a smear.    Reference 1: Japanese Laid-Open Publication No. 2000-252452